The present invention relates to intraocular lenses, and, more particularly, to intraocular lenses having variable optical properties.
The crystalline lens of the eye is susceptible to, among other impairments, the growth of cataracts. In this condition, the light that would normally pass through the lens to the retina is blocked by the clouded lens.
Various ailments including cataractous tissue growth in the lens can necessitate or desirably be treated by the removal of the crystalline lens of the eye. The natural lens thereafter is replaced with an artificial lens referred to as an intraocular lens ("IOL"). Although the development of IOL's provided significant relief for some patients, the known IOL's only imperfectly mimic the functioning of the natural lens. For example, artificial lenses are generally not elastic like the crystalline lens of the eye and cannot alter their focusing power like the normal crystalline lens of the eye. As a result, the known IOL's generally do not permit continuous adjustment of the focal power of the lens.
Some attempts have been made to provide an intraocular lens that has a variable accommodation. One approach is to provide an IOL with multiple lens surface each with a different radius of curvature. These multi-focal lenses utilizes the same principles as multi-focal eye glasses which enable the user to look through different portions of the lens to achieve different levels of diopter power. However, the levels of diopter power are fixed with the different radii of curvature of the lens surfaces and do not provide for variable levels of focusing power.
Another common approach to varying the focus of an IOL is to form a conventional hard intraocular lens with a flexible outer surface made from a material such as silicone. Water is then injected in between the conventional hard portion of the lens and the flexible outer surface of the lens. The water will stretch the outer flexible layer to change the radius of curvature of the intraocular lens and thereby change the accommodation of the lens. One disadvantage of this approach is that a fluid source, a fluid pump and a flow control valve all must be provided within close proximity to the lens. As the area around the crystalline lens of the eye is quite confined, most of the fluid injection components have to be provided on the lens itself. Further, an energy source must be provided to pump the fluid. As there is no mechanical force generated in the eye that is strong enough to pump the fluid, an external power supply is required to run the pump. Such an external power supply is usually implemented using a battery which has a limited life cycle.
A further approach that has been used to vary the accommodation of an IOL is the coating of a conventional IOL with a liquid crystal material. A voltage source is applied to the crystal material to polarize the crystals. Once the crystals are polarized the refractive index of the crystalline material changes thereby changing the accommodation of the IOL. One principal disadvantage of this type of system is the relatively large amount of energy that is required to polarize the liquid crystal material, on the order of 25 volts. As there is no known manner of generating that level of voltage within the body, an external power source, such as a battery, is therefore necessary.
The above described and other prior attempts to provide an intraocular lens with variable accommodation are generally complex systems. These complex systems are costly to manufacture and often times impractical to implement in the eye of a human. In addition, the above systems require external power sources, such as batteries, which have a limited life cycle and may require surgery to replace. Therefore, a need exists for a simple IOL with variable accommodation that only relies on the forces provided by the human body for operation.